Starting on defining manager state machines for nameplates, mailboxes, the
PAKE key-establishment process, and the bit that knows it can drop the
connection when both nameplates and mailboxes have been released.
With this, both clients and servers will send a PING at least once every
minute, and will drop connections that haven't seen any traffic for 10
minutes.
This should help keep NAT table entries alive, and will drop connections
that are no longer viable because their NAT entries have expired.
closes#60
(one displayed message per received welcome["motd"])
There's not much value in prohibiting the server from sending multiple
MOTD messages, and it would prevent us from using it to display a "your
client is using an old API, please upgrade" message after having already
sent a regular "please donate" MOTD message. (We could send a second
welcome message with ["error"] to kill the client, but ["motd"] is the
most convenient way to deliver a non-fatal warning).
The reasoning is that this string is only ever likely to refer to the
version of the primary/initial client (the CLI application, written in
Python, that you get with "pip install magic-wormhole"). When there are
other implementations, with unrelated versions, they should obviously
not pay attention to a warning about the other implementation being out
of date.
This gives us room in the future to put other keys there, like one which
says we want to use Noise for the phase-message encryption instead of
our current HKDF scheme.
This better reflects the purpose of the message. Key confirmation is a
side-effect.
This patch only changes the "phase:" name and the key-derivation string.
A subsequent patch will modify the function and variable names to match.
This should enable forwards-compatibility with clients which send extra
data, like a pre-PAKE "auxdata" message that hints we should spin up a
tor client (because they can connect to it) while we're waiting for the
user to type in the wormhole code.